N,N,N',N'-Tetramethylethylenediamine → 6'-Bromospiro[cyclopentane-1,3'-indolin]-2'-one

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n-Butyl lithium (2.5 M in hexanes, 3.8 mL, 9.5 mmol) was added dropwise over 30 minutes to a stirred suspension of 6-bromoindolin-2-one (preparation 1, 1.00 g, 4.7 mmol) and N,N,N′,N′-tetramethylethylenediamine (1.42 mL, 9.4 mmol) in tetrahydrofuran (20 mL) at −78° C. The mixture was stirred for 1 hour, then 1,4-diiodobutane (3.11 mL, 23.6 mmol) was added dropwise over 5 minutes. The mixture was warmed to −20° C. over a 1 hour period, was stirred for a further hour at this temperature and was then warmed to room temperature. After 3 hours stirring at room temperature, saturated aqueous ammonium chloride solution was added to the reaction and the mixture was extracted with ethyl acetate. The organic layer was washed with water, brine, dried (MgSO4) and evaporated. Purification of the residue by flash chromatography (10:1 hexanes/ethyl acetate) gave the title compound (0.57 g, 45%) as a pale pink solid.

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